Agricultural combines are large machines that harvest, thresh, separate and clean the agriculturally planted harvested crop which carries corn. The clean corn obtained in this way is stored in a corn tank on the combine. Rotary combines use one or two rotors enclosed in a rotor housing as a harvested crop processing arrangement to thresh and separate the harvested crop. The rotors are provided with a charging section that accepts harvested crop that had been harvested from the field, a threshing section to thresh the harvested crop received from the charging section and a separating section to release the corn that is still contained in the harvested crop after the threshing in the threshing section. During the rotation of the rotor the harvested crop is moved in the longitudinal direction from the charging section through the threshing section of the rotor to the separating section. In the separating section the axial movement of the harvested crop is obtained from helically shaped guide rails that are arranged underneath the cover element of the rotor housing. Hybrid combines are also known in which a threshing drum is arranged in the transverse direction upstream of one or two separating rotors which operates on the tangential flow principle. These are used to separate the corn from the threshed out harvested crop that are comparable to the separating section of the rotors of the rotary combines in their configuration and function.
The dwell time of the harvested crop in the separating rotor or the separating section of the crop processing unit is a function of the slope of the guide rails, that is, the positioning angle between the guide rails and the radius of the rotor. The number and the positioning angle of the guide rails are optimized for a certain volume throughput of harvested crop so that at a predetermined volume throughput a maximum separating capacity can be attained. Since many kinds of harvested crop can be accompanied by a significantly lower proportion of straw than other kinds of harvested crop, and the proportion of straw also is a function of the variable height of cut, in many cases the predetermined volume throughput is not reached. If less than the predetermined volume throughput runs through the separating rotor or the separating section, the harvested crop can run through the separating rotor or the separating section faster than desired to the end of the separating rotor or the separating section, and a large proportion of corn is lost to the harvesting process. Therefore in the case of low straw proportions or low throughput values it may be useful to exchange the cover elements of the separating rotor or the separating section (see EP 0 631 716 A) or to change the slope of the guide rails or the length of path over which they are in contact with the harvested crop (see U.S. Pat. No. 4,244,380 A, U.S. Pat. No. 4,258,726 A and the subsequently published DE 10 2006 040 979 A). Both of these possibilities are costly technically and subject to operator error.
DE 35 37 959 A which is seen as forming a class describes a combine with a tangential threshing drum that is followed by a separating rotor which is provided with two groups of guide rails that follow each other alternately. In order to avoid a jam resulting from the impact of the harvested crop upon the guide rails, the leading ends of a group of guide rails are provided with a ramp and are offset to each other in the circumferential direction, while the trailing ends of both groups lie in a straight line. The slope of the guide rails is dimensioned in such a way that the leading ends of each group of guide rails coincide with the trailing ends of each group of the following guide rails in the axial direction of the rotor.
What is needed in the art is a harvested crop processing unit of the kind cited initially that makes it possible by simple ways to permit harvested crop throughput values lower than a predetermined value to obtain sufficient dwell time in the harvested crop processing unit.